[ts-7000] COM2 serial problem on TS-7260

["yetanotherdjmorris" <>]

I have a TS-7260 trying to communicate with an RS232 device (a motor).
I can open my port, set my baud, send data to the device, the motor moves, 
sends a response back, which I can read.
Then I start a polling loop where I continually call
iReturn = ioctl(fd, FIONREAD, &iBytesAvail)
and then sleep for 20ms.
Eventually (like after 100 iterations), this returns -1
with an errno = EIO  (input/output error).
I can close the port and reopen and it works, but again, only for a few seconds 
before I get that error again.

Any thoughts?

source code:
int fd = open("/dev/ttyAM1", O_RDWR | O_NOCTTY | O_NDELAY);
        if (fd == -1)
        {
                printf("fail opening\n");
                return -1;
        }

    struct termios port_settings;
    
    cfsetispeed ( &port_settings, B9600 ) ;
    cfsetospeed ( &port_settings, B9600 ) ;

    port_settings.c_cc[VMIN] = 0 ;
    port_settings.c_cc[VTIME] = 0 ;

        port_settings.c_iflag=0;  // no input processing
        port_settings.c_oflag=0;  // no output processing
        port_settings.c_lflag=0;  
        port_settings.c_cflag=189; //8N1, 9600 baud
        

    tcflush( fd, TCIOFLUSH ) ;
        tcsetattr ( fd, TCSANOW, &port_settings ) ;
        tcgetattr (fd, &port_settings);  // make sure that the settings were 
accepted

        printf("%d %d %d %d\n", port_settings.c_cflag, port_settings.c_lflag, 
port_settings.c_iflag, port_settings.c_oflag);
        
        int iCount=0;
        int iBytesAvail, iReturn;

        unsigned char command[6]={0,2,0,0,0,0};  //packet to tell my motor to 
return home

        
        //command[0]=1;
        //command[1]=55; //echo
        //command[2]=254;

        iReturn=write(fd, command, 6);
        printf("written\n");
        sleep(2);
        iReturn = ioctl(fd, FIONREAD, &iBytesAvail);  //checks the file 
described by iFileDescriptor to see how many bytes are available, stores in 
iBytesAvail
        printf("%d bytes avail\n", iBytesAvail);
        if (iBytesAvail >=6) {
                iReturn = read(fd, &command, 6);
                printf("%d bytes read\n", iReturn);
        }

        while (iCount<1000) {
                usleep(20000);
                iReturn = ioctl(fd, FIONREAD, &iBytesAvail);  
                if (iReturn==-1) {
                        printf("Error: %d. %s\n", errno, strerror(errno));
                        return -1;
                }
                printf("%d\n", ++iCount);
        }
        close(fd);
        return 0;
}

output:
------------------------
yes?
189 0 0 0
189 0 0 0    <--- settings are  as expected
written      <--------wrote the data
12 bytes avail  <----response is available
6 bytes read    <----- read the first half of it
6 bytes read    <----- read the second half of it
1 
2             <-----------waiting for more data
3
...
284
285
Error: 5. Input/output error      <------- EIO




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